In fairness, for things like "engaged" or "married" Facebook promotes the heck out of those events making them very much a "big event you should be excited about".

If you're a decent human being, you should be happy for a past partner celebrating an important moment in their life. If they're happy, would you not be happy for them?

Can't edit this post, and I know its against the rules to mention downvotes (sorry dang!), but y'all be some bitter people. That makes me sad.